Grinding machine



June 12, 1951 M. A. HOLLENGREEN ETAL 2,556,843

GRINDING MACHINE l1 Sheets-Sheet 1 Filed July 7, 1944 Snucntcr MILBURN A. HOLLENGREEN HAROLD E. BALS/GER MA UR/CE S. GJESDAHL tqdmrucj June 12,V 1951 i M. A. HoLLENGRl-:EN ETAL 2,556,843

GRINDING MACHINE Filed July 7, 1944 l1 Sheets-Sheet 2 Summer M/LBuQ/v AHOLLENGREEN HAROLD E, BALSIQER 5g MAURICE 5. GJESU//L June 12; 1951' M. A. HoLLENGREr-:N ET AL 2,556,843

GRINDING MACHINE 11 Sheets-Sheet 5 Filed July 7, 1944 Summer MILBURN A. HLLENGFPEEN HARQLD E. ,BALS/GER MAUR/CE S. Ga/SDAHL June 12, 1951 M. A. HoLLl-:NGREEN ET AL 2,556,843

GRINDING MACHINE Filed July 7, 1944 11 Sheets-Sheet 4 June 12! 1951 M. A. HoLLl-:GREEN ETAL GRINDING MACHINE Filed July 7, 1944 11 SheetS-Sheei'l 6 M/B N A. HLLENGREEN Hmeo 5. BALS/GER MAUR/c5 s. GdEsDAHL Bnvcntor June 12l 1951 M. A. HOLLENGREEN ET AL 2,556,843

GRINDING MACHINE Filed July 7, 1944 11 sheets-sheet 7 Bnvcntor M/LBURN A. HoLLE/vqREEN HAROLD E. BALS/GER 5M MAUR/CE 5. GJESDAHL June l2, 1951 M. A. HOLLENGREEN Erm. 2,556,843

GRINDING MACHINE ll Sheets-Sheet 9 Filed July 7, 1944 ITBII 31.111.352 unix-9i. I.

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fnl/.BURN A HoLLE/vqREE/v HHROLD 'E- BALSIQEE 59 MAURICE s. GJESDA/L June l2, 1951 M. A. HOLLENGREEN ET Al. 2,556,843

GRINDING MACHINE Filed July '7, 1944 l1 Sheets-Sheet l0 FE1 E June 12,. 1951 M. A. HOLLENGREEN ET A1. 2,555,843

GRINDING MACHINE Filed Ju1y '7, 1944 11 sheds-sheet 11 Enventor M/LBURN A. HOLLENGREEN HARoL 5. BALS/65 B11 MdR/CE s. Gag-SDA /IL Patented June 12, 1951 GRINDING MACHINE Milburn A. Hollengreen, Harold E. Balsiger, and

Maurice S. Gjesdahl, Waynesboro, Pa., assignors to Landis Tool Company, Waynesboro, Pa.

Application July 7, 1944, Serial No. 543,780

The invention relates to metal working machines and more particularly to an abrasive machine of the type used for grinding screw threads on work pieces.

The usual method of grinding a thread on a work piece is to mount the same on centers and subject it to the action of a grinding wheel having either a single or multiple grooved and ridged peripheral surface. The work is rotated and traversed pastrthe grinding wheel in a manner similar to that of chasing threads on a lathe.

It is the purpose of this invention to provide a centerless grinding machine for grinding threads. Such a machine for grinding threads would make available for thread grinding all the advantages of the centerless grinding method.

So far as it is known, no one has ever offered to the general trade a practical and successful centerless thread grinder. Our invention provides a machine which has proven in actual use its ability to grind threads accurately, quickly and on a practical basis.

An object of the invention is to provide a centerless grinding machine which is so constructed as to form and shape threads on a Work piece to a desired standard.

A further object of the invention is to provide a centerless grinder wherein the grinding Wheel proper has parallel annular ridges with grooves therebetween which are shaped so as to form threads on a work piece to a desired standard.

A further object of the invention is to provide a centerless grinder of the above type wherein the Work rest is tilted relative to the axis of the grinding wheel to an angle substantially corresponding t the helix angle of the thread to be formed on the work piece.

A further object of the invention is to provide a centerless grinder of the above type having a tilted Work rest wherein the axis of the control wheel is tilted relative to the grinding wheel to an angle substantially corresponding to double the helix angle of the standard thread to be formed on the work piece.

A still further object of the invention is to provide a centerless grinder of the above type having annular ridges on the grinding wheel thereof with means for shaping said ridges so as to form and shape threads on the Work piece to a desired standard.

These and other objects will in part be obvious and will in part be hereinafter more fully disclosed.

In the drawings:

Figure 1 is a front elevation,

3 Claims. (Cl. 51-103) Figure 2 is a plan view.

Figure 3 is a right hand end elevation.

Figure 4 is a partial front elevation partly in section.

Figure 5 is a partial left end elevation partly in section.

Figure 6 is a sectional elevation of the wheel feed mechanism.

Figure 7 is a partial end elevation of the wheel forming mechanism. l

n Figure 8 is a front elevation partly in section of the wheel forming mechanism.

Figure 9 is an enlarged view of a thread sec-4 tion showing method of determining shape of wheel grooves. f

Figure 10 is an enlarged view of a screw thread showing method of determining spacing of grooves on grinding wheel. Y

Figure 11 is a view showing a formed control wheel and its angular position relative to the work and the grinding wheel.

FigureY 12 is a view showing a plain surfaced control wheel and the angular position thereof relative the grinding wheel and the Work piece.

Figure 13 shows an arrangement by which both wheels may be formed at the same time and the speed of the rotating parts synchronized.

Figure 14 is a wiring diagram.

Figure 15 is a hydraulic diagram.

Figure 16 shows the path of the work relative to the grinding wheel. y

Figure 17 shows the vertical position of .the work piece at the beginning and at the end of the grinding operation.' Y

Figure 18 is a partial plan view of a dressing mechanism for dressing the control wheel.

Figure 19 is a partial front view of a dressing mechanism for dressing the control wheel.

This invention comprises a bed having a work rest or other support mounted directly thereon, a grinding wheel unit movably mounted at one side of the work rest and a control wheel unit movably mounted at the otherside of the'work rest.

The invention has to do with a centerless grinder which is so constructed as to form or shape threads ona work piece to a desired standard. The machine, in the preferred form illus-` trated, includes a grinding wheel having annular ridges with grooves therebetween on the periphery thereof, which ridges and grooves are so shaped as to produce during the grinding operation threads on a work piece of a desired standard. Cooperating with this grinding wheel is a control wheel which is spaced therefrom so as to provide a throat for the work piece. Said control wheel is driven at a lower speed than the grinding wheel so as to cooperate with the grinding wheel in rotating and feeding the work piece. A work rest is placed between the grinding wheel and the control wheel on which the work is supported and moved during the grinding operation. Ihis work support is stationary and has a smooth supporting surface so that the work piece may be moved freely thereon. The work rest is tilted at an angle to the axis of the grinding wheel so that the ridges on the grinding wheel will properly engage or form the threads on the work piece resting on the work support for the shaping of the threads to a desired standard. This angle of the work rest relative to the axis of the grinding wheel correspends substantially to the helix angle of the thread. The axis of the control wheel is likewise inclined to the axis of the grinding wheel so that the feeding action on the work piece through contact of the control wheel therewith is a forward feed of the work piece at a rate which will permit the grinding wheel to grind evenly on both sides of a thread. This angle of the axis of the control wheel relative to the axis of the grinding wheel corresponds substantially to double the helix angle of the thread and feeds at-the rate of one or more full thread per revolution of the work piece.

While the machine herein shown and described has the grinding wheel, control wheel, and work holder or work rest arrangement generally in a horizontal plane, it will be understood that these units could be equally well arranged in vertical relation or at any intermediate angle so that the work piece will rest entirely or to a varying degree upon the control wheel and the work holder will merely position the workpiece in proper relation in the grinding throat between the wheels.

Grinding wheel mounting-Referring more in detail to the drawings, the bed of the machine is indicated at IQ. The grinding wheel base is slidably mounted thereon for movement toward and from a work piece indicated at l2. The grinding wheel unit includes a grinding wheel l5 rotatably mounted on said base Said grinding wheel may be moved toward and from working position by means of a screw 2l?, rotatably mounted in said wheel support and engaging a nut 2| secured to said bed. Said screw may be rotated by means of hand wheel 25 acting thru a diierential transmission not shown, a shaft 25 having a worm gear 2l thereon meshing with the teeth of a worm wheel 23 on said screw. Shafts 26 may be rotated either by means of hand wheel 25 or by a handle 29 in ring 3| which may be clamped to hand wheel E5 by means of a clamping bolt 30. The range of movement of handle 29 may be determined by any suitable arrangement of stop devices. The grinding wheel l5 is driven by a motor |48 on the wheel base.

The wheel base l! may be tilted at a slight angle as shown in Figure 3. This has the eiect of increasing the range of helix angles which may be accommodated on the machine.

A series of annular grooves l@ is formed between ridges Il on the face of wheel I5. The formof these grooves is slightly different than the form of the thread to be ground since the thread of the work piece is a continuous helical curve and the line joining the corresponding points of contact between wheel and work on opposite faces of a thread is not parallel with the axis of the screw thread and differs inA length from a line joining corresponding points on opposite faces of a thread in a plane containing the axis of the screw. The length of this line and the angle of the groove may be determined by means of the disclosures in Figures 9 and 10 in which the line N-N which is parallel to the axis of the grinding wheel I5 is spaced angularly from the axis of the work by the helix angle. Considered in plan view, the angles ONiXi and ONzXg are right angles by construction. Therefore the lines 0X1 and 0X2 are the hypotenuses or long sides of the two triangles. The combined line X1X2 represents the width of the V of the thread on the work piece along a plane thru its axis. The other two sides ONi and ONZ are the short sides of the triangles and the combined line NiNz represents the width of a groove on the grinding wheel and on the wheel forming tool. Hereafter reference will beY made only to the ridges on the grinding wheel.

The angle at the apex of the ridges on wheel I5 as well as on crusher H3 may be determined by means of the diagram shown in Figure 9 in which:

Angles ccb, oab, and oac are right angles. Angle A-= 1/2 angle at apex of thread mzzl/2 angle at apex of ridge on wheel Tan 11:@ ao

Tan An:g ao

ac Cos B :gl-E

where angle B is the helix angle Control wheel-A control wheel 35 is rotatably mounted on a wheel base 3B and driven thru a V belt drive by a variable voltage motor 31. Said motor is energized by a variable voltage generator mounted in the bed of the machine and adjusted by means of' a rheostat, also in the bed, the handle of which is identified by numeral 40. Wheel 35 on base 36 may be adjusted angularly in a horizontal plane for grinding tapered surfaces or in a vertical plane for effecting an axial feeding movement of a work piece for thru feed grinding operation. Said control wheel may be adjusted toward and away from the grinding wheel for work pieces of various diameters. Said control wheel may also be moved axially either manually or by power. The means for effecting the above adjustments consists of a member 55 pivotally mounted at 46 and slidable on bed l0 for angular adjustment thereon. The pivot member 46 is set in preloaded ball bearings 41 in order to provide a rigid mounting. Angular adjustment of member 45 is effected by means of screw 48 one end of which is rotatably mounted in the bed Il), the other end of which is threaded` and inserted in a nut e9 in member 45. Integral with member 45 is a cylinder 5l! in which is slidably mounted a piston 5| having a piston rod 52 one end of which is threaded. Said threaded` end has a hollow hexagonal portion 54 into which a wrench may be inserted for rotating said piston rod. Said threaded end 53 nts a nutY 53 which is secured to a slide member 55. A lock nut 54 serves to lock slide 55 in adjusted' position relative to piston 5|.

Member has formed thereon two upwardly facing `bearing surfaces, 56 and 51, oneV and one fiat respectively. Member has corresponding V and nat surfaces and 6| respectively for engaging surfaces 56 and 51 on member 45.

Member 55 has a pair of upwardly facing guide surfaces extending transversely to those on the underside thereof. One of these guides has a curved surface instead of the conventional V. The other guide 66 has a flat surface. A member 61 having a curved surface 68 for mating with guide 65 is secured to the underside of control wheel base 30 by means of screws 69.

The fiat guide 65 has slidably mounted thereon a rectangular block 15 in which is inserted a hardened button 16. A vertical adjusting screw 11 threaded in a nut 13 in base 36 rests on said button.' The upper end of said screw extends thru the top of base and has a hollow hexagonal portion 19 into which a wrench may be inserted for turning same. A sleeve 80 on said screw is graduated in terms of angles to which the control wheel may be tilted. A clamp for said screw consists of a setscrew 8| having a beveled point 82. One end of a pin 83 engages the surface of screw shaft 11, the other end has a beveled point 84 in contact with point 82.

In Figure 11 is shown an alternate type of control wheel, said wheel 245 has ridges 246 and grooves 241 practically identical with those formed on the grinding wheel I5. For most thread grinding jobs a smooth faced control wheel is adequate and superior. However on some work such as that having a large diameter, the ridged surface is helpful in feeding and in maintaining proper control of rotation of a work piece. As with the plain surface control wheel, the axis of the grooved wheel must be tilted in accordance with the helix angle with respect to the axis of the work. The ridges of the control wheel assist in maintaining the proper axial relation between the screw threads of the work piece and the ridges -of the grindingwheel |5. The endwise adjustment of wheel base 36 may be used to effect proper lateral relation between the ridges of the grinding wheel and those of the control wheel. Y

Feed mechanism-control wheeZ.-The means for adjusting the control wheel toward and from the grinding wheel consists of a feed screw 90 one end of which is threaded in a nut 9|. Said nut is mounted on a bracket 92 which in turn is mounted on slide 55. The other end of said screw is supported in base 36 on spaced ball bearings 93 and 04. worm wheel 85 is mounted on said screw shaft. A worm gear 85 on shaft 81 engages said worm wheel. A handwheel 88 on shaft 81 serves as a means for turning said shaft gears and screw for adjusting base 36 and control wheel 35 toward and from the grinding wheel |5.

Work rest-The work supporting device consists of a base member Ill) mounted directly on bed I0. Said base is slotted to receive a work supporting bar Said bar has a work engaging surface inclined in the direction of the control wheel. Work pieces are held in position just before and after the grinding operation in the case ofthru feed grinding by means of guides i I2 pivotally mounted on the base IU and urged toward the work by resilient means not shown.

Adjusting screws |22 serve to adjust bar vertically to an angular position relative to the axis of the grinding or control wheels. For grinding screw threads, said bar must be tilted Between said bearings a relative to the grinding wheel by an amount equal to the helix angle of the screw thread.l

Dressing device for thread grinding wheel- The Adressing device for the grinding wheel consists of a bracket |00 attached to wheel' base 'A second bracket |01 is adjustably attached to bracket |00 by means of screws |00 for angular adjustment about pivot |24 on said bracket |00.

Screwholes |55 are elongated to permit saidadjustment. A self contained wheel dressing mechanism is inserted in a cylindrical portion |02 of bracket |0|.' Said mechanism includes a cylindrical housing |03 having a anged portion |04 for resting on 'the cylindrical part |02 of bracket itil. A handle V|05' on Yportion |02 serves as a means to effect angular adjustment of housing |05. A saw'slot |635 in cylindrical portion |02 permits clamping of housing |53 in any adjusted position by means of screws |65. lSlidably mounted in housing |53 is a tubular'mem.- ber |05 having a key way |55. A key i 01 mounted inhousing |03 projects into said keyway to permit sliding of member |05 but to prevent rotation thereof. The lower portion of member |05 supports a bracket |03.` A wheel crushing tool H3 having annular ridges corresponding to the groovesV in wheel I5 is rotatably mounted in bracket |05. Said crushing tool is driven at a relatively low speed by a motor I4 connected thereto thrua exible connection |2| which permits vertical adjustment of said tool while the axis thereof remains parallel with that of the motor. While it is preferred to drive the wheel from the Crusher, it is possible to ldrive the wheel direct while the Crusher is driven. Wheel and crusher may also be driven in synchronism at the same pitch surace speed. Both control wheel 35 and crusher i I3 are driven by adjustable speed motors. The same type of motor may be used for driving grinding wheel l5 as illustrated in Figure 13. The surface speed of the grinding wheel may be synchronized with that of the Crusher by means of rheostat or by a mechanism such as that 4disclosed in Patents 2,302,304, granted November 17, 1942, and 2,287,449, granted June 23, 1942. Housing |03 may be angularly adjusted in cylinder |02 in order to place crusher ||3 in proper alignment with wheel I5. j Radial opening H8 in said housing permits insertion of a handle |05' for effecting said adjustment.

The means for adjusting said crushing tool toward and from the grinding wheel consists of a screw shaft ||5 supported at one end iii-fantifriction bearings |55 in the upper portion |05 of housing |05. A portion of said screw shaft extends beyond said bearings and has a graduated 'disk ||1 keyed' thereto. Radial openings H in said disk permit the insertion of a handle |04 to turn same and hence the screw l5. A hanged sleeve H9 attached to one end of tubular member E05 Ais threaded internally to engage the Ythreads of screw |i5. In order to prevent back lash in said mechanism another internally threaded member |25 is slidably mounted in member |05. A pin |25 in member |05 extends into a slot |21 in member |25 to prevent rotation thereof. Said member |25 is held resiliently in spaced relation with sleeve H0 by means of a spring |28 thus preventing backlash between said threaded members. If necessary, bracket ||l| may be adjusted in a vertical plane about pivot 2 by means of screw |20. The purpose of this adjustment is to assure parallelism 'between the axes of the Crusher IE5 and the grinding wheel I5. Bracket |0| is secured to bracket |00 by means of screws |09. The screw holes |09 in bracket are elongated to permit adjustment of bracket |0| relative to bracket |00.

Occasionally it is desirable to dress wheel by passing a diamond dressing tool across the surface of said wheel. This may be done as shown in Figure 4 by mounting a diamond dressing tool in any suitable manner on control wheel base 36. Said dressing tool consists of a bracket 230 mounted on base 36 and having a .diamond holding portion 23| extending into a position from which a diamond 232 can engage grinding wheel i5. Said base 36 may be shifted by means of hand wheel 88 and associated parts in order to position said diamond relative to wheel I5.

In order to form both the grinding wheel and the control wheel either simultaneously or separately with a single forming roller, a crushing tool H3 may be rotatably mounted in any suitable manner between the two abrasive wheels.

Said crushing tool is driven by a motor ||4 the speed of which is controlled by rheostat 95. The control wheel motor 31 and rheostat |52 have already been referred to. The grinding wheel l5 is driven by an adjustable speed motor 96 controlled by a rheostat 91.

Dressing device for control wheel-The means for dressing the control wheel consists of a diamond holder in the form of a block mounted on the rear of one of the guides |2. Said block has a diamond tool |23 removably mounted therein in position to engage the surface of control wheel 35.

Hydraulic features-The hydraulic system Consists of a motor 59 for providing the traverse movement of control wheel slide 55. Fluid under pressure is supplied by a pump driven by motor |3|. Flow of iluid in said system is held uniform by pressure operated relief valve |32 in conjunction with throttle valve |33, as described in copending application Ser. No. 524,948, led March 3, 1944, which issued as Patent No. 2,419,940.

Said fluid under pressure passes from valve |33 thru line |35 and reversing valve |40. Said reversing valve directs fluid to one side or the other of cylinder 56 thru lines |36 and |31. The rate of now thru said reversing valve is controlled by a throttle valve |34 which is built into valve |40.

Electrical equipment-The electrical equipment on our machine is disclosed diagrammatically in Figure i4 and includes a grinding wheel motor |40, an oil pump motor |3|, a generator drive motor |92, a coolant pump motor |43, a variable voltage generator |44 driven by motor |42 and a variable voltage motor 31 for driving control wheel and supplied by said generator |44. This variable voltage drive is similar to that shown in Elberty application Patent No. 2,315,511, granted April 6, 1943, and consists essentially of a series generator ills having series fields and and |5i and a rheostat |52 for varying the output of said generator. Such generator is connected to a series type motor 31 having a series field and a resistor |56 which may be set for a predetermined motor speed, in this case a speed suitable for dressing the control wheel and which is substantially higher than the range of speeds used for grinding which are determined by the rheostat 52. Another variable voltage motor referred to previously drives forming roller I3.

Alternating current is supplied to motors |3|, |49, |42 and |43 from lines I, 2 and 3 thru suitable relays. Said relays are energized by cur- 8 l rent at a lower voltage than that used on the motors. Said current is supplied from lines and 3 thru atransformer |60 to lines `|6| and |62. A master start switch |63 and a master stop switch |64 are inserted in line |6|. Line |62 is a return line.

A selector switch |10 may be set to determine which motors should be in operation for each of the conditions of setting up, grinding, forming and dressing. The grinding wheel motor |49 is controlled by a relay |15 `actuated by a coil |16. One Contact |11 of said relay is connected to a normally open contact |118 in relay |19. Said relay controls oil pump motor 3| and is actuated by coil |89. A normally closed contact I8| in relay |19 includes the rheostat |52 in the variable voltage generator. Said rheostat is set for driving control wheel 35 at a predetermined speed for grinding. Contact |18 in relay |19 when closed completes a circuit which includes resistor |56 in the eld circuit of control wheel motor 31. The purpose of this circuit is to drive said control wheel at a relatively high speed for dressing.

A third relay having a coil |86 controls the generator driving motor |42 and coolant pump motor |43 which are connected in parallel. Lines |31 and |89 supply the primary of transformer 2|0. The transformer secondary 2|| supplies rectifier 2|2 in the variable voltage drive cir cuit for control wheel 35.

Motor H9 for driving forming roller H3 is a variable voltage motor and is connected in parallel with control wheel drive motor 31. Said motors are controlled by a relay 229 actuated by a coil 22|. In the normal position of the relcy as shown contacts 222 are closed, to complete the circuit which includes control wheel motor 31. When coil 22| is energized contact 223 is closed and 222 opened. The control wheel motor 31 is thus stopped and forming tool motor ||4 is started.

Operation In order to start the machine, the operator presses master start button |63. This energizes coil of relay |9I to close said relay and complete the circuit to selector switch |19. Said relay also establishesI a holding circuit for coil |90.

Set zip-The rst step in the operation of this invention is to set up, that is to arrange the various parts to machine a specific work piece. For this operation, the only motor which might be needed is the oil pump motor 53|. By closing contact |1| of selector switch |13, current is directed thru line 200 to energize coil |80 of relay |19 which closes the circuit to oil pump motor |3|. The control wheel 35 is adjusted toward grinding wheel |5 by turning hand wheel '8B until said Wheel is in position for a work piece of the desired size. This is determined by adjusting wheel 35 until the work piece has moved up the inclined surface of bar` so that the center of the work is in the desired position relative to the plane of the axes of the two wheels l5 and 35. Work supporting bar must be adjusted angularly relative to the grinding wheel axis by an amount equal to the helix angle of the threads on the piece to be ground so that the ridges |1 of wheel l5 will properly form threads on work piece l2. This adjustment may be accomplished by means of adjusting screws |22. f

Control wheel base 36 must be tilted relative to the grinding wheel I5 to an angle equal substantially to double the helix angle. It may be slightly more than double the helix angle. Tilting the control wheel 35 to double the helix angle has the effect of giving the work I2 the proper rate of axial feed per revolution for the helix angle of the thread being ground. This angle is `fixed. for any given screw. However, by changing the speed of the control wheel, the production rate of the machine may be changed. A slight additional tilt is effective to overcome friction between the work and work rest. This last is desirable but not essential.

If it is desired to grind a tapered work piece, wheel 35 may be so adjusted by turning screw 48 until the desired taper is indicated on a graduated plate 4I on member 45.

Wheel dressing-In this machine the only operation resembling dressing which occurs at reg- .ular intervals during the grinding of a given size of thread is that of forming or crushing the grinding wheel I5. However it is sometimes desirable or necessary to dress the faces of both the grinding and control wheels. This is particularly true when new wheels have been placed on the machine or when the setup is changed for work of a different size.

For performing this dressing operation the operator turns selector switch tothe position marked dress. In this position circuits are closed at contacts |14, |141 and |142 to energize relays |15, |19 and |35 respectively. Relay |15 controls the grinding wheel motor |43. Relay |19 controls oil pump motor |3I. Relay |85 controls generator drive motor |42 and coolant pump motor |43. When wheel motor relay .is energized, contacter |11 closes a circuit which includes contacter |18 of oil pump. relay |19.

Thus when relay |19 is energized the circuit thru 1 contacter |18 is closed. This circuit includes resistor |56 in the field of control wheel motor 31. The effect of closing this circuit'is to increase the speed of motor 31 and hence of control wheel 35 to a speed suitable for dressing. The operator turns hand wheel 8B to withdraw wheel 35 to a position in alignment with diamond |23. Valve |46 is then turned to direct uid under pressure to one side of cylinder 5|). Piston 5I then moves wheel support 35 and wheel 35 past diamond |23. Valve I4@ is turned in the opposite direction to return said wheel to its original position. The rate of movement of said piston and wheel support is determined by throttle valve |34 which is built into valve |40. If it is desirable or necessary to dress grinding wheel I5, diamond 232 may be used. Said diamond is mounted on bracket 230 on wheel base 36. The traverse movement described above may be used to pass said diamond across wheel Because of the relative angular positions of the control wheel, the work rest and the plane of movement of wheel support 36 during a grinding operation, the matter of dressing said wheel along the path of travel of the work presents somewhat of a problem.

Assuming the grinding wheel I5 to be in a vertical plane, the work rest blade I|I will be inclined relative to the grinding wheel axis by an amount substantially equal to the helix angle of the thread to be ground. The control wheel 35 must be tilted relative to the work rest by an amount substantially equal to the helix angle and is thus tilted or inclined relative to the grinding wheel by an amount substantially equal to double the helix angle.

The elevation of the work I2 and hence the lo point at which to begin dressing the control wheel I5 must be determined with all the parts -in operative position. The center of the work should be above the center of the wheel I5 by an amount such that the axes of said wheel and the work Will be in intersecting planes at the end of the grinding throat. The diamond may be adjusted to a gauge or simply to a mark made by rubbing the work against the surface of said wheel while at rest, said work rests on the work support bar after said bar has been adjusted to place the work in the desired position relative to the wheel centers.

The path of the work begins preferably above the center of the grinding wheel at the entrance kto the throat and intersects the plane thru the grinding wheel axis as it leaves said throat. These conditions must be the same regardless of whether the grinding wheel is directly above the control wheel or in some other angular relation thereto. This provides a throat which becomes narrower as the work moves along its path. Generally the path of travel of the work relative to the grinding wheel may be described as follows. The path of travel of the work across the grinding wheel is a line ab intersecting the plane which contains the Wheel axis and the point b where the work leaves the wheel, the angle of intersection being the helix angle of the screw thread to be ground. This is illustrated in Figures 16 and 17. Actually the line a-b is not a straight line because it follows the curvature of the wheel thru a sho-rt distance as it moves thru the grinding throat. However, the actual path is so nearly a straight line that it is diiiicult to see or show the diiference on a small scale drawing.

From the above, it would be apparent that the method of producing finished screw threads on work pieces in a centerless grinder, whether the work pieces be unthreaded or whether they have pre-cut threadsthereon, consists in providing a grinding wheel with annular ridges thereon, a control wheel and a work support having a smooth surface on which the work piece is free to move endwise, spacing the controll wheel from the grinding wheel so as to provide avgrinding throat, arranging the axes of the wheels in substantially parallel planes and inclined in opposite directions with respect to said work rest at an angle thereto substantially equal to the helix angle, positioning the work rest so that the grinding throat has a minimum width at the exit end thereof measured from the bottom of the grinding wheel grooves to the surface of the control wheel substantially equal to the diameter of the finished work piece, placing the work piece to be ground on the work rest and rotating and moving said work piece endwise through the throat solely by the action of the grinding wheel and control wheel operating through their frictional contact with the work piece.

During dressing, the control wheel moves in a horizontal direction. During grinding the work moves at an angle to the grinding wheel axis equal to the helix angle. The work also moves at the same angle to the control wheel which is double the helix angle from the grinding wheel axis. In order to dress along this path on the control wheel, said wheel must be tilted so that its axis is parallel to the surface of the work rest or to the axis of the work. The diamond is adjusted to the previously marked position referred to above and the control wheel i1 is passed across it making a path thereon which is spaced angularly from the axis of said wheel by the amount of the helix angle. After dressing, said wheel is tilted back to double the helix angle and the path of the diamond across the face thereof will be parallel to the axis of the work.

The third step in preparation for a. grinding operation is to form the grinding wheel I5. This is done by a method known as crushing. Selector switch Il@ is turned to the forming position. In this position contacts Il'2 and H21 are closed. Contact Il? is in the circuit to generator motor relay 185. Contact H21 is in the circuit to relay 22E. When energized, said relay opens the circuit to control wheel motor 3l and closes the circuit to crusher motor H4. Oil pump motor I3I is not in operation at this time and therefore normally closed contactor I8I in relay I'IQ completes a`circuit which includes rheostat H52 in generator iield IEB. This rheostat controls the grinding or slow speed of the motor 3i and therefore of Crusher motor I Id also.

Crusher roller H3 may be fed toward grinding wheel i any predetermined amount as indicated on disk IIT. Said disk may be rotated by means of a handle inserted in radial holes H8. Said disk is keyed to screw H5. When said screw is turned, member It and forming roller I I3 move toward or away from the grinding wheel I5. Rotation of roller IIS causes rotation of wheel I5, the result of this rolling together being that the forming tool produces its contour on the grinding tool I5. If particles or" dirt or grit lodge in the grooves of roller H3 an inaccurate thread may be formed. In order to prevent this, a brush 24o mounted in the fender portion of base II engages said grooved surface and removes all particles therefrom.

After wheel I5 has been formed, switch ITB is turned to the grinding position. In this position contact H3 is closed to start the grinding wheel motor |411. Contact H3 is also closed. This contact is connected to contact |12 which controls the generator motor H42 to drive control wheel motor 37. Work pieces are introduced into the grinding throat. Sometimes the work tends to rise from the rest due to the action of the control wheel. come by any suitable hold down device.

As soon as a work piece I2 is introduced into the grinding throat, the action of the grinding wheel I5 urges said work piece against the control wheel. The control wheel 35 then rotates the work; and, because of the angular relation of said control wheel with the smooth work rest I2, it not only rotates the work piece, but moves it endwise at a rate of one or more full threads per revolution. The control wheel 35 provides the sole feeding means of the work piece through the grinding throat; and in the case of a prethreaded work piece, this rate of feed prevents the ridged grinding wheel from functioning as a nut, and thus the ridges on the grinding wheel serve neither to advance nor to retard the endwise movement of the work piece. If the feeding action of the control wheel is too great, the leading iianks of the threads will be ground too heavy. If the feeding action of the control wheel is too little, the work piece will have to provide a part of the endwise movement by its threading action with the ridges of the grinding wheel; and the trailing iianks of the thread will be ground too heavy. In

This may be overf either case, the result is an inaccuracy in lead. With the control wheel set at the helix angle of the screw to be ground, relative to the work rest, the rate of feed of the work is independent of any threading action between the Work and the ridges of the grinding wheel; and maximum lead accuracy is attained.

We claim:

1. The method of generating screw threads of a predetermined helix angle on a substantially cylindrical workpiece in a centerless grinding machine having a grinding wheel with annular ridges thereon, a control wheel peripherally opposed to said grinding wheel and spaced therefrom to form a grinding throat, and a smooth surface work rest for supporting the workpiece for movement between the opposed portions of said wheels, which consists in arranging the axes of said Wheels in substantially parallel planes and inclined in opposite directions With respect to said work rest at an angle thereto substantially equal to said helix angle, and with the peripheral faces of said wheels spaced from each other to provide a grinding throat having a minimum width measured from the bottom of the grinding wheel grooves to the surface of the control wheel substantially equal to the diameter of the workpiece, supporting a cylindrical workpiece on the work rest with its axis maintained parallel with the smooth surface thereof, rotating the workpiece solely by the driving and controlling effect of the grinding and control wheels and simultaneously moving the workpiece endwise through the throat in predetermined timed relation with the rotation solely by the action of the grinding and control wheels operating through their frictional contact with the workpiece.

2. The method of producing finished screw threads on work pieces of a predetermined helix angle in a centerless grinding machine having a grinding wheel with annular ridges thereon, a control wheel peripherally opposed to the grinding wheel and spaced therefrom to form a grinding throat, and a smooth surface work rest for supporting the work piece for movement between the opposed portions of said wheels, which consists in arranging the axes of the wheels in substantiallyparallel planes, and inclined in opposite direction with respect tothe work rest at an angle thereto substantially equal to the helix angle, said work rest being positioned relative to the axis of the grinding wheel so as to provide a grinding throat which is progressively narrower from the entrance end to the exit end thereof, the width at its exit end being substantially equal to the diameter of the nished workpiece, supporting a workpiece on the work rest and rotating the workpiece solely by the driving and controlling effect of the grinding and control wheels for simultaneously moving the workpiece endwise into and through the grinding throatk in predetermined timed relation with the rotation solely by the action of the grinding and control wheels operating in frictional contact with the workpiece.

3. A centerless grinding machine for producing finished screw threads of a predetermined helix angle on workpieces comprising a grinding wheel having annular ridges thereon, means for rotating said grinding wheel, a control wheel peripherally opposed to said grinding wheel and spaced therefrom to form a grindingY throat, means for rotating said control wheel, a smooth surface work rest for supporting,l a workpiece UNITED STATES PATENTS, for free endwise movement through said grind- Number Name Date ing throat, said work rest beiner inclined rel- 1 528 188 Frost Mar. 3 1925 ative to the axis of the grinding wheel at an 1302260 Hanson Feb. 12 1929 angle substantially equal to the helix angle of 5 1,845,885 Einstein et a1 Een 16J 1982 the screw to be produced so that a thread will 2,010,730 L1Oyd Aug 6, 1935 be formed having a shape substantially con- 2116031 Lindner M51y 3l 1938 forming to said annular' ridges of the grinding 2 122 184 Scrivener June 28, 1938 wheel, the axis of said control wheel being in 2,135,202 Scrive'ner N0v 1, 1933 clined in the same direction as the work rest l0 3,236,045 Wickman June 9I 1942 and at an angle thereto substantially equal to 2,402,454 50111/81161. June 19J 1946 the helix angle of the screw so that a workpiece will be fed solely by the control wheel endwise FOREIGN PATENTS along said smooth work rest at a rate of one Number Country Date or more full threads per revolution to produce l5 248,893 Great Britain Mar. 18, 1926 a finished thread on the workpiece of the desired 516,259 Great Britain Dec. 28, 1939 predetermined helix angle.

MILBURN A. HOLLENGREEN. OTHER REFERENCES HAROLD E BALSIC-TER Grinding Wheels'ahnd Their Uses by John- MAURICE S GJESDAHL. 3;; son Heywood, 1st Edition, published 1938 by The Penton Publishing Company, Cleveland, Ohio, REFERENCES CITED pages 215 to 217, inclusive.

The following references are of record in the file of this patent: 

